FinFET structure and fabricating method of gate structure

ABSTRACT

A method of forming a gate structure on a fin structure includes the steps of providing a fin structure covered by a first silicon oxide layer, a silicon nitride layer, a gate material and a cap material in sequence, wherein the silicon nitride layer contacts the first silicon oxide layer. Later, the cap material is patterned to form a first cap layer and the gate material is patterned to form a first gate electrode by taking the silicon nitride layer as an etching stop layer. Then, the silicon nitride layer not covered by the first gate electrode is removed to expose part of the first silicon oxide layer. Finally, a first dielectric layer is formed to conformally cover the first silicon oxide layer, the first gate electrode and the first cap layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of and claimspriority to U.S. patent application Ser. No. 15/284,552, filed on Oct.4, 2016, and entitled “FINFET STRUCTURE AND FABRICATING METHOD OF GATESTRUCTURE” the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of fabricating a gatestructure, and more particularly to a method of fabricating a gatestructure by using an additional silicon nitride layer.

2. Description of the Prior Art

In recent years, the semiconductor industry has experienced exponentialgrowth, particularly in the pursuit of higher device density andperformance with lower cost. A classical planar transistor cannotachieve such goals, however, due to physical constraints.

Accordingly, various non-planar transistors, such as fin-likefield-effect transistors (FinFETs), have been introduced to replaceplanar transistors. Although existing FinFETs and methods of fabricatingFinFETs have been adequate for their intended purposes, they have notbeen entirely satisfactory in all respects. With high demand for scalingdown the FinFET size, manufacturing methods must be continuouslyimproved to obtain a more satisfactory FinFET structure.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a FinFETstructure includes a fin structure and a first gate structure disposedon the fin structure. The first gate structure includes a first gateelectrode, a first silicon oxide layer contacting the fin structure, asilicon nitride layer contacting the silicon oxide layer and a firstgate dielectric layer disposed between the first gate electrode and thesilicon nitride layer. The FinFET structure further includes a secondgate structure disposed on the fin structure. The second gate structureincludes a second gate electrode, a second silicon oxide layer and asecond gate dielectric layer between the second gate electrode and thesecond silicon oxide layer. The second gate dielectric layer does notcover the silicon nitride layer and the first silicon oxide layer. TheFinFET structure further includes first source/drain doped regionsdisposed in the fin structure at two sides of the first gate electrodeand second source/drain doped regions disposed in the fin structure attwo sides of the second gate electrode.

According to another preferred embodiment of the present invention, amethod of forming a gate structure on a fin structure includes the stepsof providing a fin structure covered by a first silicon oxide layer, asilicon nitride layer, a gate material and a cap material in sequence,wherein the silicon nitride layer contacts the first silicon oxidelayer. Later, the cap material is patterned to form a first cap layerand the gate material is patterned to form a first gate electrode bytaking the silicon nitride layer as an etching stop layer. Then, thesilicon nitride layer not covered by the first gate electrode is removedto expose part of the first silicon oxide layer. Finally, a firstdielectric layer is formed to conformally cover the first silicon oxidelayer, the first gate electrode and the first cap layer.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 9 depict a method of forming a gate structure on a finstructure according to a preferred embodiment of the present invention,wherein:

FIG. 1 is a fabricating stage of providing a fin structure;

FIG. 2 is a fabricating stage following FIG. 1;

FIG. 3 is a fabricating stage following FIG. 2;

FIG. 4 is a fabricating stage following FIG. 3;

FIG. 5 is a fabricating stage following FIG. 4;

FIG. 6 is a fabricating stage following FIG. 5;

FIG. 7 is a fabricating stage following FIG. 6;

FIG. 8 is a fabricating stage following FIG. 7;

FIG. 9 is a three dimensional diagram of FinFET structures.

DETAILED DESCRIPTION

FIG. 1 to FIG. 9 depict a method of forming a gate structure on a finstructure according to a preferred embodiment of the present invention,wherein FIG. 9 is a three dimensional diagram of FinFET structuresfabricated by the method provided in the present invention. As shown inFIG. 1, at least one fin structure 10 is provided. The fin structure 10protrudes from a substrate 12. Refer to FIG. 9 for the position of thesubstrate 12. Referring back to FIG. 1, the number of the fin structure10 can be adjusted based on different requirements. The fin structure 10includes a first region A and a second region B. The operational voltageof a device within the first region A is higher than the operationalvoltage of a device within the second region B.

A first silicon oxide layer 14, a silicon nitride layer 16, a gatematerial 18, and a cap material 20 are formed to cover the first regionA and the second region B on the fin structure 10 from bottom to top.The silicon nitride layer 16 contacts the first silicon oxide layer 14.The first silicon oxide layer 14 may be formed by an in situ steamgeneration process. The gate material 18 may be polysilicon, amorphoussilicon, silicide or other materials which can serve as a dummy gate.The cap material 20 may be a stacked layer such as a silicon nitridelayer 22 and a silicon oxide layer 24. The first silicon oxide layer 14is silicon oxide. The silicon nitride layer 16 is silicon nitride.

As shown in FIG. 2, the cap material 20 and the gate material 18 arepatterned by taking the silicon nitride layer 16 as an etching stoplayer to form a first cap layer 26 and a first gate electrode 28 withinthe first region A, and to form a second cap layer 126 and a second gateelectrode 128 within the second region B. In detail, the first cap layer26 and the second cap layer 126 are formed by etching the cap material20. The first gate electrode 28 and the second gate electrode 128 areformed by etching the gate material 18. Because the silicon nitridelayer 16 serves as an etching stop layer, the first silicon oxide layer14 under the silicon nitride layer 16 is protected by the siliconnitride layer 16 while etching the cap material 20 and the gate material18. The surface of the first silicon oxide layer 14 will therefore notbe damaged by the etchant when etching the cap material 20 and the gatematerial 18.

As shown in FIG. 3, the silicon nitride layer 16 not covered by thefirst gate electrode 28 and the second gate electrode 128 is removed toexpose part of the first silicon oxide layer 14. The silicon nitridelayer 16 can be removed by a clean process such as a clean process usingphosphoric acid as a clean solution. As shown in FIG. 4, a firstdielectric layer 30 is formed to conformally cover the first siliconoxide layer 14, the first gate electrode 28, the second gate electrode128, the first cap layer 26 and the second cap layer 126. The firstdielectric layer 30 is preferably silicon carbon nitride. Then, at leastone first implantation process is performed to implant dopants into thefin structure 10 to form first lightly doped regions 32 in the finstructure 10 at two sides of the first gate electrode 28 and secondlightly doped regions 132 in the fin structure 10 at two sides of thesecond gate electrode 128. The conductive type of the first lightlydoped regions 32 and the second lightly doped regions 132 may be thesame or different.

The first lightly doped regions 32 and the second lightly doped regions132 can be formed simultaneously if the first lightly doped regions 32and the second lightly doped regions 132 are of the same conductivetype. If the first lightly doped regions 32 and the second lightly dopedregions 132 are different conductive types, they should be formed by twoseparate implantation processes. The dopants can be P-type dopants orN-type dopants. The conductive type of the first lightly doped regions32 and the second lightly doped regions 132 may be the same ordifferent.

As shown in FIG. 5, a spacer 34 and a spacer 134 are formed torespectively surround the first gate electrode 28 and the second gateelectrode 128. Later, at least one second implantation process isperformed to implant dopants into the fin structure 10 to form firstsource/drain doped regions 36 in the fin structure 10 at two sides ofthe first gate electrode 28 and second source/drain doped regions 136 inthe fin structure 10 at two sides of the second gate electrode 128. Theconductive type of the first source/drain doped regions 36 and thesecond source/drain doped regions 136 may be the same or different. Thefirst source/drain doped regions 36 and the second source/drain dopedregions 136 can be formed simultaneously if the first source/drain dopedregions 36 and the second source/drain doped regions 136 are of the sameconductive type. If the first source/drain doped regions 36 and thesecond source/drain doped regions 136 are different conductive types,they should be formed by two separate implantation processes. Thedopants can be P-type dopants or N-type dopants. Then, a seconddielectric layer 38 is formed blankly to cover the spacer 34, the spacer134, the first dielectric layer 30, the first cap layer 26, and thesecond cap layer 126. Subsequently, the second dielectric layer 38 isplanarized to be aligned with the first dielectric layer 30 on the topof the first cap layer 26.

As shown in FIG. 6, part of the first dielectric layer 30, part of thespacers 34 sand 134, part of the second dielectric layer 38, the entirefirst cap layer 26, and the entire second cap layer 126 are removed toexpose the first gate electrode 28 and the second gate electrode 128. Asshown in FIG. 7, the first gate electrode 28 and the second gateelectrode 128 are removed simultaneously. A first trench 40 is formedafter removing the first gate electrode 28. Later, the silicon nitridelayer 16 and the first silicon oxide layer 14 (which originally weredirectly under the second gate electrode 128) are removed. A secondtrench 42 is formed after removing the second gate electrode 128, thesilicon nitride layer 16 under the second gate electrode 128, and thefirst silicon oxide layer 14 under the second gate electrode 128. Atthis point, part of the fin structure 10 in the second region B isexposed.

In detail, the first trench 40 is defined by the silicon nitride layer16 and the first dielectric layer 30 in the first region A. The secondtrench 42 is defined by the first dielectric layer 30, and the finstructure 10 in the second region B. It is noteworthy that the firstsilicon oxide layer 14 and the silicon nitride layer 16 which originallywere directly under the first gate electrode 28 are remained.

As shown in FIG. 8, a second silicon oxide layer 44 is formed on thebottom of the second trench 42. The second silicon oxide layer 44 can beformed by a chemical deposition process, an oxidation process or anatomic layer deposition process. The second silicon oxide layer 44 issilicon oxide. After that, a first gate dielectric layer 48 such as afirst high-k dielectric material is formed at the sidewalls and thebottom of the first trench 40. A second gate dielectric layer 148 suchas a second high-k dielectric material is formed on the sidewalls of thesecond trench 42, and on the second silicon oxide layer 44. The firstgate dielectric layer 48 in the first trench 40 forms a U-shape. Thesecond gate dielectric layer 148 in the second trench forms anotherU-shape. The first high-k dielectric material may be Al₂O₃, ZrO₂, bariumstrontium titanate (BST), lead zirconate titanate (PZT), ZrSiO₂, HfSiO₂,HfSiON, TaO₂, or the like. The second high-k dielectric material mayAl₂O₃, ZrO₂, barium strontium titanate (BST), lead zirconate titanate(PZT), ZrSiO₂, HfSiO₂, HfSiON, TaO₂, or the like. The first high-kdielectric material and the second high-k dielectric material may bemade of the same material or different materials. After that, a firstwork function layer 50 is formed in the first trench 40. The first workfunction layer 50 may be TiN, TaN or other metal nitride adjustinglayer. The second work function layer 150 may be TiN, TaN or other metalnitride adjusting layer. A second work function layer 150 is formed inthe second trench 42. The first work function layer 50 and the secondwork function layer 150 may be made of the same material or differentmaterials. Later, a first metal gate electrode 52 fills in the firsttrench 40 and a second metal gate electrode 152 fills in the secondtrench 42. The first metal gate electrode 52 may be copper, aluminum,titanium, molybdenum, tantalum, tungsten or other metals. The secondmetal gate electrode 152 may be copper, aluminum, titanium, molybdenum,tantalum, tungsten or other metals. At this point, a FinFET 100 and aFinFET 200 are completed. The first metal gate electrode 52, the firstsilicon oxide layer 14 under the first metal gate electrode 52, thesilicon nitride layer 16 and the first gate dielectric layer 48 serve asa first gate structure 54. The second metal gate electrode 152, thesecond silicon oxide layer 44 and the second gate dielectric layer 148serve as a second gate structure 154.

FIG. 9 depicts a three dimensional diagram of FinFET structures. FIG. 8depicts a sectional view taken along line AA′ in FIG. 9. As shown inFIG. 8 and FIG. 9, FinFET structures 300 include a FinFET 100 and aFinFET 200.

The FinFET 100 includes a fin structure 10, a first gate structure 54disposed on the fin structure 10, first source/drain doped regions 36disposed in the fin structure 10 at two sides of the first gatestructure 54, and first lightly doped regions 32 disposed in the finstructure 10 at two sides of the first gate structure 54. The first gatestructure 54 includes a first metal gate electrode 52, a first siliconoxide layer 14 contacting the fin structure 10, a silicon nitride layer16 contacting the silicon oxide layer 14 and a first gate dielectriclayer 48 disposed between the first gate electrode 52 and the siliconnitride layer 16.

The FinFET 200 includes the fin structure 10, a second gate structure154 disposed on the fin structure 10, second source/drain doped regions136 disposed in the fin structure 10 at two sides of the second gatestructure 154, and second lightly doped regions 132 disposed in the finstructure 10 at two sides of the second gate structure 154. The secondgate structure 154 includes a second metal gate electrode 152, a secondsilicon oxide layer 44 contacting the fin structure 10, and a secondgate dielectric layer 148 disposed between the second metal gateelectrode 152 and the second silicon oxide layer 44. It is noteworthythat the second gate dielectric layer 148 does not cover the siliconnitride layer 16 and the first silicon oxide layer 14, i.e. the secondgate structure 154 does not include the silicon nitride layer 16 and thefirst silicon oxide layer 14. The first gate structure 54 includes thesilicon nitride layer 16 and the first silicon oxide layer 14.Furthermore, the first silicon oxide layer 14 is directly under thespacer 134 and the spacer 34. The thickness of the silicon nitride layer16 is preferably 10 to 30 angstroms. The thickness of the first siliconoxide layer 14 is preferably 5 to 40 angstroms. The first silicon oxidelayer 14 is silicon oxide. The silicon nitride layer 16 is siliconnitride. A first dielectric layer 30 such as a silicon carbon nitridesurrounds the first gate structure 54 and the second gate structure 154.

The first gate dielectric layer 48 may be a first high-k dielectricmaterial, and the first high-k dielectric material is U-shaped. Thefirst high-k dielectric material may be Al₂O₃, ZrO₂, barium strontiumtitanate (BST), lead zirconate titanate (PZT), ZrSiO₂, HfSiO₂, HfSiON,TaO₂, or the like. The second gate dielectric layer 148 may be a secondhigh-k dielectric material, and the second high-k dielectric material isalso U-shaped. The second high-k dielectric material may be Al₂O₃, ZrO₂,barium strontium titanate (BST), lead zirconate titanate (PZT), ZrSiO₂,HfSiO₂, HfSiON, TaO₂, or the like. The first gate dielectric layer 48and the second gate dielectric layer 148 may be made of the samematerial or different materials.

The fin structure 10 further includes a first region A and a secondregion B. The operational voltage of a device within the first region Ais higher than the operational voltage of a device within the secondregion B. The FinFET 100 is disposed within the first region A, and theFinFET 200 is disposed within the second region B. The FinFET 100 mayserve as a high voltage device such as an input/output (IO) transistor,and the FinFET 200 may serve as a low voltage device such as a coretransistor.

Conventionally, the cap material 20 and the gate material 18 arepatterned by using the first silicon oxide layer 14 as an etching stoplayer. The quality of the first silicon oxide layer 14 will be damagedafter the patterning process, however, and the etchant will flow intothe damaged part of the first silicon oxide layer 14 to harm the bottomcorner of the gate electrode formed by the gate material 18. The presentinvention utilizes a silicon nitride layer 16 as an etching stop layerwhile patterning the cap material 20 and the gate material 18. In thisway, the first silicon oxide layer 14 under the silicon nitride layer 16can be protected by the silicon nitride layer 16 during the patterningprocess.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method of forming a gate structure on a finstructure, comprising: providing a fin structure covered by a firstsilicon oxide layer, a silicon nitride layer, a gate material and a capmaterial in sequence, wherein the silicon nitride layer contacts thefirst silicon oxide layer; patterning the cap material to form a firstcap layer and patterning the gate material to form a first gateelectrode by taking the silicon nitride layer as an etching stop layer;removing the silicon nitride layer not covered by the first gateelectrode to expose part of the first silicon oxide layer; and forming afirst dielectric layer conformally covering the first silicon oxidelayer, the first gate electrode and the first cap layer.
 2. The methodof forming a gate structure on a fin structure of claim 1, furthercomprising: patterning the cap material to form a second cap layer andpatterning the gate material to form a second gate electrode whileforming the first cap layer and the first gate electrode; removing thesilicon nitride layer not covered by the second gate electrode whileremoving the silicon nitride layer not covered by the first gateelectrode; and forming the first dielectric layer conformally coveringthe second gate electrode and the second cap layer while forming thefirst dielectric layer conformally covering the first silicon oxidelayer, the first gate electrode and the first cap layer.
 3. The methodof forming a gate structure on a fin structure of claim 2, furthercomprising: forming first lightly doped regions and second lightly dopedregions in the fin structure at two sides of the first gate electrodeand at two sides of the second gate electrode by taking the firstdielectric layer, the first cap layer, and the second cap layer as amask; forming a first spacer surrounding the first dielectric layer onthe first gate electrode, and a second spacer surrounding the firstdielectric layer on the second gate electrode; and forming firstsource/drain doped regions at two sides of the first gate electrode andforming second source/drain doped regions at two sides of the secondgate electrode by taking the first dielectric layer, the first caplayer, the second cap layer, the first spacer and the second spacer as amask.
 4. The method of forming a gate structure on a fin structure ofclaim 3, further comprising: forming a second dielectric layer coveringthe first dielectric layer, the first cap layer, the second cap layerand the fin structure; removing part of the second dielectric layer, theentire first cap layer and the entire second cap layer to expose thefirst gate electrode and the second gate electrode; removing the firstgate electrode to form a first trench; removing the second gateelectrode, the silicon nitride layer directly under the second gateelectrode, and the first silicon oxide layer directly under the secondgate electrode to form a second trench; forming a second silicon oxidelayer at a bottom of the second trench; forming a first gate dielectriclayer conformally covering the first trench; forming a second gatedielectric layer covering the sidewalls of the second trench and thesecond silicon oxide layer; and forming a first metal gate in the firsttrench and a second metal gate in the second trench.
 5. The method offorming a gate structure on a fin structure of claim 1, wherein thefirst dielectric layer is silicon carbon nitride.